Fix: properly decouple from pyplot and specific backends when destroying

When destroying a manager, replace the figure's canvas by a
figure canvas base.

Author: timhoffm

lib/matplotlib/backend_bases.py

@@ -2723,7 +2723,9 @@ def show(self):
             f"shown")
 
     def destroy(self):
-        pass
+        # managers may have swapped the canvas to a GUI-framework specific one.
+        # restore the base canvas when the manager is destroyed.
+        self.canvas.figure._set_base_canvas()
 
     def full_screen_toggle(self):
         pass

lib/matplotlib/backends/_backend_gtk.py

@@ -195,6 +195,7 @@ def destroy(self, *args):
         self._destroying = True
         self.window.destroy()
         self.canvas.destroy()
+        super().destroy()
 
     @classmethod
     def start_main_loop(cls):

lib/matplotlib/backends/_backend_tk.py

@@ -606,6 +606,7 @@ def delayed_destroy():
         else:
             self.window.update()
             delayed_destroy()
+        super().destroy()
 
     def get_window_title(self):
         return self.window.wm_title()

lib/matplotlib/backends/backend_gtk3.py

@@ -89,6 +89,7 @@ def __init__(self, figure=None):
 
     def destroy(self):
         CloseEvent("close_event", self)._process()
+        super().destroy()
 
     def set_cursor(self, cursor):
         # docstring inherited

lib/matplotlib/backends/backend_gtk4.py

@@ -90,6 +90,7 @@ def __init__(self, figure=None):
 
     def destroy(self):
         CloseEvent("close_event", self)._process()
+        super().destroy()
 
     def set_cursor(self, cursor):
         # docstring inherited

lib/matplotlib/backends/backend_nbagg.py

@@ -137,6 +137,7 @@ def _create_comm(self):
         return comm
 
     def destroy(self):
+        super().destroy()
         self._send_event('close')
         # need to copy comms as callbacks will modify this list
         for comm in list(self.web_sockets):

lib/matplotlib/backends/backend_qt.py

@@ -664,6 +664,7 @@ def show(self):
             self.window.raise_()
 
     def destroy(self, *args):
+        super().destroy()
         # check for qApp first, as PySide deletes it in its atexit handler
         if QtWidgets.QApplication.instance() is None:
             return

lib/matplotlib/backends/backend_wx.py

@@ -1007,6 +1007,7 @@ def show(self):
     def destroy(self, *args):
         # docstring inherited
         _log.debug("%s - destroy()", type(self))
+        super().destroy()
         frame = self.frame
         if frame:  # Else, may have been already deleted, e.g. when closing.
             # As this can be called from non-GUI thread from plt.close use

lib/matplotlib/figure.py

@@ -2642,7 +2642,7 @@ def __init__(self,
         self._set_artist_props(self.patch)
         self.patch.set_antialiased(False)
 
-        FigureCanvasBase(self)  # Set self.canvas.
+        self._set_base_canvas()
 
         if subplotpars is None:
             subplotpars = SubplotParams()
@@ -2996,6 +2996,15 @@ def get_constrained_layout_pads(self, relative=False):
 
         return w_pad, h_pad, wspace, hspace
 
+    def _set_base_canvas(self):
+        """
+        Initialize self.canvas with a FigureCanvasBase instance.
+
+        This is used upon initialization of the Figure, but also
+        to reset the canvas when decoupling from pyplot.
+        """
+        FigureCanvasBase(self)  # Set self.canvas as a side-effect
+
     def set_canvas(self, canvas):
         """
         Set the canvas that contains the figure

lib/matplotlib/tests/test_backends_interactive.py

@@ -227,12 +227,15 @@ def check_alt_backend(alt_backend):
     # Ensure that the window is really closed.
     plt.pause(0.5)
 
-    # Test that saving works after interactive window is closed, but the figure
-    # is not deleted.
+    # When the figure is closed, it's manager is removed and the canvas is reset to
+    # FigureCanvasBase. Saving should still be possible.
     result_after = io.BytesIO()
     fig.savefig(result_after, format='png')
 
-    assert result.getvalue() == result_after.getvalue()
+    if backend.endswith("agg"):
+        # agg-based interactive backends should save the same image as a non-interactive
+        # figure
+        assert result.getvalue() == result_after.getvalue()
 
 
 @pytest.mark.parametrize("env", _get_testable_interactive_backends())